1. Field of the Invention
The present invention relates to a split heat exchanger, and particularly to a radiator with maximized entering temperature differentials for both at least one charge air cooler and a jacket water cooler.
2. Description of the Related Art
It is well known that heat energy contained in one fluid is capable of being transferred to another fluid. Such heat transfer is described in the classical heat transfer equation: Q=UAdT. In this equation, Q represents the heat transfer, U represents a coefficient of heat transfer, A represents the surface area through which the heat can be transferred, and dT represents the change in temperatures between the two mediums. Heat exchangers, and radiators in particular, are designed for a relative high level of transfer of heat energy from one medium to another. One common example is an automobile radiator, in which a coolant fluid passes through an engine to absorb heat energy from the engine. The coolant fluid then is routed through the radiator, where heat is transferred from the coolant fluid to the environment (ambient air).
Engineers and designers have incorporated many strategies to increase the amount of heat that a heat exchanger is capable of transferring. One strategy is to attempt to increase the coefficient of heat transfer. Design components, such as the incorporation of louvers, dimples, waves, ridges and other alterations to the fin profiles have been effectively used. While these improvements are quantifiable and generally useful, there are limitations (both practical and theoretical) as to how much the coefficient of heat transfer can be improved. For example, the increased tooling costs may overshadow any savings associated with the increased coefficient. Accordingly, it may take a long time to recapture those costs through efficiency savings, if it is even possible at all.
Others have had success in increasing the heat transferring capability of the heat exchanger by increasing the surface area between the two mediums (i.e. increasing the size of the heat exchanger). The increases in surface area can come from a combination of increases in height, width, depth and density of the heat exchanger. Often times, the size requirements for shipping and use dictate maximum dimensions in the height and width dimensions. In such situations, the only remaining variable is the depth of the unit. Accordingly, designers have increased the depth of the heat exchanger in order to increase the surface area.
Some heat exchangers are designed for use with engines having turbochargers. It is standard practice to stack two or more radiators in series to cool both a jacket water coolant from the engine and charge air compressed by one or more turbochargers. One configuration has a charge air cooler first, and a jacket water cooler second. Put another way, the charge air cooler is upstream of the jacket water cooler in some configurations, such that air first passes through the charge air cooler and second through the jacket water cooler. There are several drawbacks associated with such standard arrangements.
First, having a series stacked heat exchanger has a depth that is equal to the depth of both the jacket water cooler and the charge air cooler. Such a design has a depth that is often greater than that of a single radiator. Any additional depth can increase the system resistance, which is caused when pressure develops between the fan or air mover and the rear side (down stream side) of the jacket water cooler. Pressure can develop by expansion of the air as it gains energy from the heat exchanger, and also by overcoming obstructions to the free flow of the air. The fan therefore needs to have greater horsepower capacity (i.e. higher initial cost plus increased energy consumption during operation) in order to move the intended amount of air through the heat exchanger to overcome the increase in system pressure.
A further drawback of such an arrangement is that the ambient air first passes through the charge air cooler, and then passes through the jacket water cooler. The air enters the charge air cooler at ambient temperature (the maximum temperature differential). Heat energy is transferred from the charge air to the environmental air, such that the environmental air leaving the charge air cooler is warmer than the air entering the heat exchanger. The environmental air at an elevated temperature then enters the jacket water cooler where it again receives energy, this time transferred from the engine coolant. Yet, the air entering the jacket water cooler has a temperature above the ambient air temperature. Accordingly, the temperature differential between the coolant and the air is less than maximum, and the energy transfer is less than maximum. Such a design is disadvantageously engineered to be less than optimally efficient.
A still further drawback of the stacked system is that for dual turbocharged engines, a manifold is required to route the charge air through the charge air cooler. Several drawbacks can be associated with the use of a manifold. First, it would be undesirable if the return manifold did not evenly distribute the cooled charge air back to both sides of the engine. Second, the charge air can suffer from a pressure loss as it passes through the torturous paths of the manifold and other required piping. Pressure loss of the charge air during routing to and from the charge air cooler reduces the net effect of the turbochargers. Third, the piping and plumbing can add to the overall complexity of the design and manufacturing of the heat exchanger, and the piping and plumbing can be inconvenient to access.
It is well know that axial fans have a “dead” spot where the hub rotates due to the lack of air being driven. Non-uniform air flow rates in an axial direction are caused by the “dead” spots. The standard stacked arrangement prohibits mechanical compensation for different air flow rates across the front face of the heat exchanger due to the dead spot. Accordingly, some portions of the heat exchanger are capable at operating at higher efficiency relative the other portions making the overall heat transfer efficiency less than ideal. The zone of the dead spot and associated inefficiency is more profound downstream of the first heat exchanger where stacked arrangements are used.
Thus there exists a need for a heat exchanger that solves these and other problems.